Thank you for visiting nature.com. You are using a browser version with
limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off
compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site
without styles and JavaScript.

Abstract

Symbiotic relationships are widespread in terrestrial and aquatic animals today, but evidence of symbiosis in the fossil record between soft-bodied bilaterians where the symbiont is intimately associated with the integument of the host is extremely rare. The radiation of metazoan life apparent in the Ediacaran (~635–541 million years ago) and Cambrian (~541–488 million years ago) periods is increasingly accepted to represent ecological diversification resulting from earlier key genetic developmental events and other innovations that occurred in the late Tonian and Cryogenian periods (~850–635 million years ago). The Cambrian has representative animals in each major ecospace category, the early Cambrian in particular having witnessed the earliest known complex animal communities and trophic structures, including symbiotic relationships. Here we report on newly discovered Cricocosmia and Mafangscolex worms that are hosts to aggregates of a new species of tiny worm in the lower Cambrian (Series 2, Stage 3) Chengjiang Lagerstätte of Yunnan Province, southwest China. The worm associations suggest the earliest known record of aggregate infestation of the integument of a soft-bodied bilaterian, host specificity and host shift.

Acknowledgements

The reconstruction in Fig. 4 was produced by R. Nicholls (http://paleocreations.com). The research was funded by the National Natural Science Foundation of China (41572015 and U1302232), a Natural Environment Research Council Independent Research Fellowship (NE/L011751/1), Leverhulme Trust grants (RPG-2015-441 and EM 2014‐068), a Royal Society International Joint Project (IE131457) and a Yunnan Innovation Research Team grant (2015HC029).

Search for Gregory D. Edgecombe in:

Search for Xianguang Hou in:

Contributions

P.C. and X.M. conceived the project and led the team. P.C., X.M., X.H. and D.Z. collected and prepared the specimens. T.G., S.E.G., G.D.E. and P.C. conducted the scanning electron microscop and element mapping analyses. Derek J.S. and P.C. photographed the specimens and prepared the figures. M.W. and P.C. produced the camera lucida drawings. X.M. calculated the infestation rates. All authors interpreted the data. M.W. and David J.S. wrote the initial draft with scientific and editorial input from P.C., X.M., G.D.E., S.E.G. and Derek J.S.